X-Message-Number: 25603 Date: Fri, 21 Jan 2005 10:29:41 -0800 (PST) From: Doug Skrecky <> Subject: modulating telomeres [Telomeres shortened by reducing KU86 or DNA-PKcs, but not PARP-1.] J Cell Biol. 2004 Nov 22;167(4):627-38. Epub 2004 Nov 22 Impact of telomerase ablation on organismal viability, aging, and tumorigenesis in mice lacking the DNA repair proteins PARP-1, Ku86, or DNA-PKcs. The DNA repair proteins poly(ADP-ribose) polymerase-1 (PARP-1), Ku86, and catalytic subunit of DNA-PK (DNA-PKcs) have been involved in telomere metabolism. To genetically dissect the impact of these activities on telomere function, as well as organismal cancer and aging, we have generated mice doubly deficient for both telomerase and any of the mentioned DNA repair proteins, PARP-1, Ku86, or DNA-PKcs. First, we show that abrogation of PARP-1 in the absence of telomerase does not affect the rate of telomere shortening, telomere capping, or organismal viability compared with single telomerase-deficient controls. Thus, PARP-1 does not have a major role in telomere metabolism, not even in the context of telomerase deficiency. In contrast, mice doubly deficient for telomerase and either Ku86 or DNA-PKcs manifest accelerated loss of organismal viability compared with single telomerase-deficient mice. Interestingly, this loss of organismal viability correlates with proliferative defects and age-related pathologies, but not with increased incidence of cancer. These results support the notion that absence of telomerase and short telomeres in combination with DNA repair deficiencies accelerate the aging process without impacting on tumorigenesis. [Somatostatin boosts KU86.] Eur J Histochem. 2004 Apr-Jun;48(2):103-10 The expression and the nuclear activity of the caretaker gene ku86 are modulated by somatostatin. Somatostatin is a peptide hormone that exerts antisecretory and antiproliferative activities on some human tumors. The Ku70/86 heterodimer acts as regulatory subunit of the DNA dependent protein kinase and its DNA binding activity mediates DNA double strands breaks repair that is crucial to maintain the genetic integrity of the genome. The activation of the heterodimer regulates cell cycle progression and the activity of nuclear transcription factors involved in DNA replication and cell proliferation. Moreover Ku86 behaves as a receptor for the growth inhibitory tetradecapeptide, somatostatin. Herein we report that somatostatin treatment to a colon carcinoma cell line (Caco-2) inhibits cell growth and, at same time, strongly modulates the activation of Ku70/86 heterodimer and the levels of Ku86 in the nucleus by increasing its specific mRNA level. Our findings are consistent with the hypothesis that somatostatin controls cell cycle progression and DNA repair through a new signalling pathway that involves the regulation of Ku86 level and modulates the Ku70/86 activity in the nucleus. [Leupeptin boosts KU86.] Mutat Res. 1999 Dec 7;435(3):225-32 Senescent human fibroblasts have elevated Ku86 proteolytic cleavage activity. A proteolytic activity capable of cleaving the Ku86 subunit of Ku protein to two polypeptides, with molecular masses of 69 and 17 kDa in vitro, is present in a human diploid fibroblast (HDF) cell line. The activity is elevated in late-passaged and senescent cells, and the cleaved 69-kDa product seems able to form complex with Ku70 to bind DNA ends. However, further studies indicate that cleavage of Ku86 could be inhibited by including leupeptin in the extraction buffer, and no 69 kDa variant was evident in the cell. In fact, the levels of Ku86, Ku70 and DNA-end binding activity of Ku remained unchanged during replicative senescence. Thus, this study reveals an intriguing protease in HDFs, and also indicates that inconsistent results of Ku86 expression will be obtained if the protease activity is not completely inhibited. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=25603